Since its early development in the 1980s, the global market for wind energy has expanded exponentially. In the period between 1990-2007 the world’s total wind electricity capacity has grown 50 times and is predicted to increase over the 2008 level by ten-fold by 2030, and twenty-fold by 2050, [1]. In order to achieve the expansion expected in this area, there is a need for the development of stronger and lighter materials which will enable manufacturing of blades for larger rotors. The larger the area through which the turbine can extract the wind energy, the more power that can be captured (See Figure 1). Advanced materials with higher strength to mass ratios could enable larger area rotors to be cost-effective. Carbon nanotube based composites could enable larger rotor blades.

Figure 1. Growth in size of the rotor diameter of wind turbines since 1980. Adapted from [1].

The results obtained so far in the project Carbon Nanotube Reinforced Polyurethane Composites for Wind Turbine Blades (DE-EE0001361), demonstrate that polyurethane (PU) resins outperform the currently used resins for wind blades application. Encouraged by these results, we have decided to manufacture small scale carbon nanotube reinforced PU wind blades. Specifically, CNT reinforced PU blades 29” long have been prepared with six glass fiber mats using the vacuum bag technique. In a typical experiment, multi-walled carbon nanotubes (MWCNTs) were added to polyol and dispersed by using simultaneous sonication (Sonics CP750, 165W) and magnetic stirring during 30 min. The concentration of CNTs and dispersing agent (B60H) has been fixed at 0.05 wt% in relation to polyol. The isocyanate was added to the polyol and the system was used to wet the six layers of biax glass fabric. The steps followed during the manufacturing of the wind blades are presented in Figures 1-3 whereas the CNT reinforced PU blade obtained by vacuum bag is shown in Figure 4.

Figure 3. Vacuum bagging process: a) view of the form prototype (a commercial wind blade) on the bag after applying a layer of releasing agent. This blade was used to produce a template (mold) for the lay-up of the glass fabric imbibed in a suspension of CNTs in PU as shown in (b); c) lay-up is done. Note that the CNT-PU blades assume the same shape as the original form prototype.

Figure 4. Final steps of the vacuum bagging process: a) the releasing film is layed up over the glass fabric layers; b) the breather cloth is layed up over the releasing film; c,d) The bag is sealed on the three open sides after removing the release paper of the bag sealant tape; e) atmospheric pressure is used to hold the resin-coated components in place until the PU cures. A vacuum pump reduces the air pressure inside the bag.

Figure 5. CNT reinforced PU blade obtained by vacuum bag technique.

To the best of our knowledge these are the world’s first carbon nanotube reinforced polyurethane wind blades. The blades were installed in a 400W 12V wind turbine generator (Figure 5).

Figure 6. Blades installed in a 400W wind turbine generator.

A test of the wind turbine generator was performed and a video of the turbine working on a building roof can be seen below:

This functional prototype with CNT reinforced PU blades will be stored in our laboratory and will be used to emphasize the significant potential of CNT reinforced PU systems for use in the next generation of wind turbine blades.

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.